Rock drilling apparatuses may be used in a number of areas of application. For example, rock drilling apparatuses may be used in tunneling, underground mining, rock reinforcement, raise boring, and for drilling of blast holes, grout holes and holes for installing rock bolts, etc.
A drill tool such as, for example, a drill bit is often used during drilling, the drill bit being connected to a drilling machine, in general by means of a drill string. The drilling can be accomplished in various ways, e.g. as rotational drilling where the drill tool is pushed towards the rock at high pressure and then crushes the rock by means of rotation force and applied pressure.
Percussive drilling machines can also be used, where, for example, a piston strikes the drill string to transfer percussive pulses to the drill tool via the drill string and then further on to the rock. Percussive drilling is often combined with a rotation of the drill string in order to obtain a drilling where the buttons of the drill bit strikes fresh rock at each stroke, thereby increasing the efficiency of the drilling.
During drilling the drill tool can be pressed against the rock by means of a feed force to ensure that as much impact energy as possible from the hammer piston is transmitted to the rock.
In general, the rock drilling apparatus further includes a power source, such as, for example, a combustion engine (e.g. a diesel engine) or an electric motor, which is used to generate required power to the various functions of the rock drilling apparatus. The power that is required by the various functions of the rock drilling apparatus can be arranged to be provided mainly by one power source, such as a combustion engine or an electric motor, the power source thereby constituting a main power source.
Percussion force, rotation force, feed force, etc. are, in general, generated by means of hydraulic flows from hydraulic pumps which constitute loads of the power source and hence are driven by the power source. The power source can also power cooling fans, as well as other consumers/loads, such as means for propelling the rock drilling apparatus. The loads of the power source are often directly connected to, and hence driven by, the output shaft of the power source, i.e. the power that can be provided by the load to a consumer of the load is dependent on the rotation speed of the power source.
In general rock drilling apparatuses also include means for generating flushing pressure/flow for evacuation of the drilling remnants, the so called drill cuttings, that are generated during drilling.
This is usually accomplished by means of a flushing medium, such as, for example, compressed air, flushing air, which is led through a channel in the drill string for release through flushing air holes in the drill bit to thereafter bring the drilling remnants on its way up through the hole. The pressure/flow of the flushing medium can be generated by means of a compressor which is also driven by the output shaft of the power source. Consequently, the power that can be discharged by the compressor is also directly dependent on the rotation speed of the power source.
According to the prior art the rotation speed of the power source is controlled, in so much the speed is at all controlled, based on few input parameters. For example, the motor speed can be controlled based on chosen mode of operation, such as for example, the modes of operation movement, drilling, or drill rod handling. Also, in some situations the operator can manually set the speed of the power source for various modes of operation during operation.
The rotation speed at the various modes of operation is often chosen such that the full capacity of the drilling rig is available for all active consumers at all times at the current mode of operation. During drilling, for example, the percussion mechanism (percussion force), rotation force, feed force and flushing air. In order to ensure a correct function the power source is therefore in general dimensioned such that all functions can be used at the same time, and at their maximum output powers.
The advantages of such a solution is that one and the same power source can be used as power source for all loads/consumers occurring at the drilling rig, such as compressor, hydraulic pumps/motors, percussion mechanism etc.
However, in many situations of operation the full capacity of the loads and/or consumers is not utilized, which also means that the power source many times is driven at a speed that is not optimal.
This also means that rock drilling apparatuses often consume more power than necessary during a drilling process, which results in excessive fuel consumption and also undesired generation of heat and noise.
Consequently, there exists a need for an improved control of rock drilling processes.